The structure and mechanism of two enzyme systems (lipoxygenase and phthalate dioxygenase) are investigated using advanced forms of magnetic resonance spectroscopy (electron paramagnetic resonance and Mossbauer) to characterize their active sites. The availability of single crystals of phthalate dioxygenase reductase and phthalate dioxygenase provide an opportunity to orient the g-tensors with the [2Fe-2S] centers in these proteins, which will add precise structural implications to the spectroscopic information on all metalloproteins containing [2Fe-2S] clusters, a large and important group of proteins. The conformational distributions of these proteins will also be interpreted in terms of the new information on the spectroscopic distributions known as g-strain. This interpretation can also provide insight into the mechanism of electron transfer dynamics, which is important in most enzymatic systems. The studies on lipoxygenase from soybeans and a model compound for the active site, FeDTPA, will concentrate upon identifying a) the ligand environments of the active site in its several forms during catalysis and b) the mechanism of the enzyme-substrate interaction. Special emphasis will be on the action of various inhibitors which are important in a variety of health-related issues. As part of this effort, the EPR and Mossbauer spectra will be synthesized to obtain structural information.